In the case of an operation of an internal combustion engine of a motor vehicle, knowledge of a coolant temperature of an engine cooling system may be of great importance. For this reason, particular importance may be placed on the monitoring of one or a multiplicity of coolant temperature sensors by legislators. As a result of an erroneous or non-functioning coolant temperature sensor, the internal combustion engine can no longer be actuated in an optimum manner which can lead to increased emissions and damage up to the failure of the internal combustion engine.
For example, the monitoring, i.e., detection, of a “sticking” coolant temperature sensor is required which is carried out in the case of cooling systems with mechanical thermostats when the vehicle is at a standstill. A “sticking” coolant temperature sensor refers in this case to a temperature sensor, the measurement value of which does not change or changes only slightly over a longer time span or exhibits little dynamism in the case of its output measurement value. Such monitoring can be influenced by an auxiliary heater fitted in the motor vehicle when the internal combustion engine is started. It is furthermore desired to also diagnose sticking coolant temperature sensors during operation of the internal combustion engine.
DE 196 08 340 A1 discloses a method for controlling an internal combustion engine which checks before the internal combustion engine is started whether a preheating of the internal combustion engine is carried out by means of a block heater. A difference between a temperature of the internal combustion engine and a temperature of the intake air of the internal combustion engine serves as a measure for this. If this difference lies above a predetermined minimum value, a preheating of the internal combustion engine by means of the block heater is assumed and this is taken into account in the actuation of the internal combustion engine in the case of a current start.
The operation of an auxiliary heater is normally made available to an engine controller of the motor vehicle as information. On the basis of this information, a monitoring of the coolant temperature sensor can be influenced in a corrective manner or suppressed for a specific time, e.g. an overall driving cycle. This information is, however, not always correct when the internal combustion engine is started.
Auxiliary heaters which are retrofitted in the vehicle are furthermore problematic since their influence cannot be taken into account in advance by the manufacturer. Particularly in the case of a motor vehicle fitted with such an “After Market Product” such as e.g. with an engine block heater or a block heater, undesired or dissonant erroneous inputs in a controller can arise in the case of monitoring of the coolant temperature sensor. This can lead to a replacement of a coolant temperature sensor although it is fully functional which thus results in unnecessary costs.